1. Field of the Invention
The present invention relates to a jet mill of a horizontal turning flow type.
2. Description of the Prior Art
Recently, various types of jet mills have been developed, which are used in various fields such as generation, etc., of powder poor in heat such as agrichemicals, toner, etc., or ceramic powder and micro-crushed powder by bringing it into collision with each other by high speed jet.
For example, Japanese Patent Publication No. 16981 of 1988 (hereinafter called Publication "A") discloses "an ultrasonic jet mill in which a circumferential part of a circular separation chamber is caused to face a collision space between a collision plate opposed to the outlet of a main nozzle for high pressure gas jetting and the nozzle outlet, and the circular separation chamber are caused to communicate with the outlet side of a material feeding passage communicating with midway of the main nozzle in a bypass passage extending in the circumferential tangential direction of the circular separation chamber, and a discharge passage of micro powder is connected to the middle portion of said circular separation chamber. In addition, as a construction similar thereto, Japanese Laid-Open Patent Publication Nos. 50554 of 1982, 50555 of 1982, 50556 of 1982, 290560 of 1992, 184966 of 1993, 275731 of 1995, 152742 of 1996, 155324 of 1996, 182937 of 1996, 254855 of 1996, 323234 of 1996, Japanese Utility Model Publication Nos. 52110 of 1991, 53715 of 1995, 8036 of 1995, and Laid-Open Utility Model Publication No. 19836 of 1994 have been known.
Japanese Patent Publication No. 17501 of 1988 (hereinafter called Publication "B") discloses "a jet mill having, at one end thereof, a solid and gas blending chamber formed, in which a material feeding port and a crushed material feeding nozzle for jetting a high pressure gas are opened adjacent to each other, and, at the other end, a turning and crushing chamber is formed, in which a collision plate is provided and a crushing nozzle for jetting a high pressure gas is disposed, wherein one end of the solid and gas blending chamber is caused to communicate with one end of the turning and crushing chamber by an accelerator tube opposite to the collision plate, a screening chamber which communicates with the turning and crushing chamber is formed via a rectification zone on the outer circumference of the accelerator tube, and further an annular screening plate which encloses the accelerator tube is provided in the screening chamber with its interior communicated with the discharge hole and its exterior communicated with the solid and gas blending chamber.
Japanese Patent Publication No. 9057 of 1989 (hereinafter called Publication "C") improves the jet mill disclosed by patent "B" and discloses "a jet mill provided with a projection (center pole), the center portion of which protrudes mostly toward the center of the outlet of the accelerator, on the collision plate".
Japanese Laid-Open Patent Publication No. 254427 of 1994 (hereinafter called Publication "D") discloses "a jet mill comprising a plurality of crushing nozzles for forming turning flows by jetting a high pressure gas into a turning and crushing chamber, and a collision member provided opposite to the jetting portions of the respective crushing nozzles, wherein the collision member is a flat collision plate, the shape at the downward end and upward end along the turning flow direction of which is formed to be thin like a blade, the collision face is located in the flow direction of the turning flows, and is inclined so that an angle a formed by the collision face and the center line of the crushing nozzles opposite thereto in a range from 30 to 60 degrees, and the collision member is disposed and fixed by an attaching means, the angle of which is adjustable."
Japanese Laid-Open Patent Publication No. 111459 of 1990 (hereinafter called Publication "E") discloses "a jet mill in which the widening angle of an accelerator tube is formed to be 7 through 9 degrees." In addition, Japanese Utility Model Publication No. 25227 of 1995 is known as its equivalent.
Further, a prior art jet mill was such that crushed material feeding nozzles and jet nozzles for jetting a high pressure gas were designed and arranged so that jet nozzles are disposed at positions where the circumference of a turning and crushing chamber is equally divided, and crushed material feeding nozzles are disposed one by one between each of the two equidistantly disposed jet nozzles, wherein the total number of nozzle is designed to be an odd number.
However, the abovementioned prior art jet mill has the following shortcomings and problems;
The jet mill as set forth in Publication "A" has a problem and/or a shortcoming by which, if a crushed material, for example, a new ceramic crushed material having high hardness is brought into collision with a fixing wall in line with a jet stream of a high pressure gas, the part of the fixing wall, with which the crushed material is brought into collision, is recessed by wearing, the fixing wall is damaged in a short time, and the durability thereof is remarkably impaired.
The jet mill as set forth in Publication "B" also has a problem and/or a shortcoming similar to that of Publication "A", and another problem by which, since materials are fed to the middle portion (pressure-reduced portion) of a turning air stream, crushed micro powder may be accumulated at the middle portion to worsen the screening efficiency, and the grain size distribution is remarkably widened.
In the jet mill as set forth in Publication "C", since both feeding of crushed materials and discharge of micro powder are carried out at the upper part of the turning and crushing chamber, normal streams of the turning flows which form crushing nozzles greatly fall into disorder, such disorder of the turning flows increases pressure loss, resulting in a lowering of the speed of the turning flows, whereby the crushing capacity is decreased.
In the jet mill as set forth in Publication "D", the crushing efficiency is excellent in that a collision action effected by four collision plates secured in the turning and crushing chamber is utilized. However, the speed of the turning flows of a high speed jet is lowered due to the existence of the collision plates, and the shape of crushed powder becomes square, and such a problem arises, by which it becomes difficult to adjust the grain size distribution.
Further, if the number of prior art crushed material feeding nozzles and jetting nozzles disposed is an odd number, since, after turning flows are formed by an even number of crushing nozzles, a solid and gas multi-phase flow is pressed into the turning and crushing chamber by one crushed material feeding nozzle, such a problem arises, by which segregation of turning flows due to said solid and gas multi-phase flows pressed into later on is likely to occur, and at the same time, the high pressure gas amount of the crushed material feeding nozzles and jetting nozzles must be separately established, the operation control becomes cumbersome, whereby the operation efficiency is spoiled. In addition, since the number of nozzles is an odd number, segregation is also likely to occur, wherein another problem arises, by which the crushing efficiency and screening efficiency are impaired.
In addition, since the respective jetting nozzles are provided with only one jetting port, a turning and crushing chamber is produced on the basis of flow lines of turning flows being two-dimensionally understood and analyzed as one line. Therefore, the velocity at the upper part (top liner portion) and the lower part (bottom liner portion) of the turning and crushing chamber is lowered. Accordingly, such a problem arises, by which a stay duration of large grains in the turning and crushing chamber is made longer, and the liner portions at the upper part and lower part is remarkably worn.
Further, since adjustment of the grain size of micro powder is carried out by changing only the pressure or volume of a jet stream in either type, segregation of turning flows and pressure fitting of micro powder to the inner walls of the turning and crushing chamber are liable to occur by characteristics of crushed materials, such shortcomings and/or problems arise, which causes a remarkable wearing of liner portions such as ring liners of the turning and crushing chamber, the top liner, and bottom liner, whereby continuous stabilized operation becomes impossible.